/*
 * 将一个有音频和视频流的文件，解码出音频和视频，分别存入文件中。
 * 视频文件可以使用ffplay来播放。
 * 程序编译后，在终端运行：./Decode 01.mp4 video.yuv audio.pcm。
 * 在程序运行结束的最后会打印播放视频和音频的命令。
 */

#include "decodeandsave.h"

#ifdef __cplusplus
#define __STDC_CONSTANT_MACROS
#define UINT64_C
extern "C"
{
#endif
#include <libavutil/imgutils.h>
#include <libavutil/samplefmt.h>
#include <libavutil/timestamp.h>
#include <libavformat/avformat.h>
#ifdef __cplusplus
}
#endif

static AVFormatContext *fmt_ctx = NULL;
static AVCodecContext *video_dec_ctx = NULL, *audio_dec_ctx;
static int width, height;
static enum AVPixelFormat pix_fmt;
static AVStream *video_stream = NULL, *audio_stream = NULL;
static const char *src_filename = NULL;
static const char *video_dst_filename = NULL;
static const char *audio_dst_filename = NULL;
static FILE *video_dst_file = NULL;
static FILE *audio_dst_file = NULL;

static uint8_t *video_dst_data[4] = {NULL};
static int      video_dst_linesize[4];
static int video_dst_bufsize;

static int video_stream_idx = -1, audio_stream_idx = -1;
static AVFrame *frame = NULL;
static AVPacket pkt;
static int video_frame_count = 0;
static int audio_frame_count = 0;

static int output_video_frame(AVFrame *frame)
{
    //如果不是我们要存储的格式就忽略
    if (frame->width != width || frame->height != height ||
        frame->format != pix_fmt) {
        fprintf(stderr, "Error: Width, height and pixel format changed.\n");
        return -1;
    }

    printf("video_frame n:%d coded_n:%d\n",
           video_frame_count++, frame->coded_picture_number);

    //将图像复制到目标缓存中，video_dst_data是个4维的char*，yuv各用1个，预留1个。
    av_image_copy(video_dst_data, video_dst_linesize,
                  (const uint8_t **)(frame->data), frame->linesize,
                  pix_fmt, width, height);

    //写入到文件中
    fwrite(video_dst_data[0], 1, video_dst_bufsize, video_dst_file);
    return 0;
}

static int output_audio_frame(AVFrame *frame)
{
    //根据音频采样率、音频格式，算出一个音频采样点多少字节。
//    size_t unpadded_linesize = frame->nb_samples * av_get_bytes_per_sample(frame->format);
    size_t unpadded_linesize = frame->nb_samples * av_get_bytes_per_sample(static_cast<AVSampleFormat>(frame->format));
    printf("audio_frame n:%d nb_samples:%d pts:%ld\n",
           audio_frame_count++, frame->nb_samples,
          frame->pts);
    fwrite(frame->extended_data[0], 1, unpadded_linesize, audio_dst_file);

    return 0;
}

static int decode_packet(AVCodecContext *dec, const AVPacket *pkt)
{
    int ret = 0;

    //1.将包发给解码器，解码器内部会对其进行解码。
    ret = avcodec_send_packet(dec, pkt);
    if (ret < 0) {
        fprintf(stderr, "Error submitting a packet for decoding %d\n", ret);
        return ret;
    }

    //2.一个包可能解出多个帧，所以要用循环
    while (ret >= 0) {
        ret = avcodec_receive_frame(dec, frame);
        if (ret < 0) {
            //这两个特殊返回值意味着没有可用的输出帧，但解码过程中没有错误
            if (ret == AVERROR_EOF || ret == AVERROR(EAGAIN))
                return 0;

            fprintf(stderr, "Error during decoding %d\n", ret);
            return ret;
        }

        //3.将解码后的数据写入输出文件
        if (dec->codec->type == AVMEDIA_TYPE_VIDEO)
            ret = output_video_frame(frame);
        else
            ret = output_audio_frame(frame);

        //4.注意每次帧都要解引用，否则会认为帧还有用，最后垃圾数据特别多
        av_frame_unref(frame);
        if (ret < 0)
            return ret;
    }

    return 0;
}

static int open_codec_context(int *stream_idx,
                              AVCodecContext **dec_ctx, AVFormatContext *fmt_ctx, enum AVMediaType type)
{
    int ret, stream_index;
    AVStream *st;
    AVCodec *dec = NULL;
    AVDictionary *opts = NULL;

    //1.查找指定的流（音频流或视频流等）
    ret = av_find_best_stream(fmt_ctx, type, -1, -1, NULL, 0);
    if (ret < 0) {
        fprintf(stderr, "Could not find %s stream in input file '%s'\n",
                av_get_media_type_string(type), src_filename);
        return ret;
    } else {
        stream_index = ret;  //得到指定流的索引，保存用于返回。
        st = fmt_ctx->streams[stream_index];

        //2.查找流对应的解码器
        dec = avcodec_find_decoder(st->codecpar->codec_id);
        if (!dec) {
            fprintf(stderr, "Failed to find %s codec\n",
                    av_get_media_type_string(type));
            return AVERROR(EINVAL);
        }

        //3.构造AVCodecContext结构体对象
        *dec_ctx = avcodec_alloc_context3(dec);
        if (!*dec_ctx) {
            fprintf(stderr, "Failed to allocate the %s codec context\n",
                    av_get_media_type_string(type));
            return AVERROR(ENOMEM);
        }

        //4.把找到的对应解码器的参数复制给刚构建的AVCodecContext结构体对象
        if ((ret = avcodec_parameters_to_context(*dec_ctx, st->codecpar)) < 0) {
            fprintf(stderr, "Failed to copy %s codec parameters to decoder context\n",
                    av_get_media_type_string(type));
            return ret;
        }

        //5.打开解码器并初始化
        if ((ret = avcodec_open2(*dec_ctx, dec, &opts)) < 0) {
            fprintf(stderr, "Failed to open %s codec\n",
                    av_get_media_type_string(type));
            return ret;
        }
        *stream_idx = stream_index;
    }

    return 0;
}

static int get_format_from_sample_fmt(const char **fmt,
                                      enum AVSampleFormat sample_fmt)
{
    int i;
    struct sample_fmt_entry {
        enum AVSampleFormat sample_fmt; const char *fmt_be, *fmt_le;
    } sample_fmt_entries[] = {
        { AV_SAMPLE_FMT_U8,  "u8",    "u8"    },
        { AV_SAMPLE_FMT_S16, "s16be", "s16le" },
        { AV_SAMPLE_FMT_S32, "s32be", "s32le" },
        { AV_SAMPLE_FMT_FLT, "f32be", "f32le" },
        { AV_SAMPLE_FMT_DBL, "f64be", "f64le" },
    };
    *fmt = NULL;

    for (i = 0; i < FF_ARRAY_ELEMS(sample_fmt_entries); i++) {
        struct sample_fmt_entry *entry = &sample_fmt_entries[i];
        if (sample_fmt == entry->sample_fmt) {
            *fmt = AV_NE(entry->fmt_be, entry->fmt_le);
            return 0;
        }
    }

    fprintf(stderr,"sample format %s is not supported as output format\n",
            av_get_sample_fmt_name(sample_fmt));
    return -1;
}

int main_decode_save (int argc, char *argv[])
{
    int ret = 0;

    if (argc != 4) {
        fprintf(stderr, "usage: %s  input_file video_output_file audio_output_file\n",
                argv[0]);
        exit(1);
    }
    src_filename = argv[1];
    video_dst_filename = argv[2];
    audio_dst_filename = argv[3];

    //1.打开文件
    if (avformat_open_input(&fmt_ctx, src_filename, NULL, NULL) < 0) {
        fprintf(stderr, "Could not open source file %s\n", src_filename);
        exit(1);
    }

    //2.从文件中提取流信息
    if (avformat_find_stream_info(fmt_ctx, NULL) < 0) {
        fprintf(stderr, "Could not find stream information\n");
        exit(1);
    }

    //3.打开视频解码器并初始化，得到解码视频的AVCodecContext结构体对象
    if (open_codec_context(&video_stream_idx, &video_dec_ctx, fmt_ctx, AVMEDIA_TYPE_VIDEO) >= 0) {
        video_stream = fmt_ctx->streams[video_stream_idx];

        //打开保存视频数据的输出文件
        video_dst_file = fopen(video_dst_filename, "wb");
        if (!video_dst_file) {
            fprintf(stderr, "Could not open destination file %s\n", video_dst_filename);
            ret = 1;
            goto end;
        }

        //得到宽、高、像素格式，根据这些来分配具体一张图片的内存空间
        width = video_dec_ctx->width;
        height = video_dec_ctx->height;
        pix_fmt = video_dec_ctx->pix_fmt;
        ret = av_image_alloc(video_dst_data, video_dst_linesize,
                             width, height, pix_fmt, 1);
        if (ret < 0) {
            fprintf(stderr, "Could not allocate raw video buffer\n");
            goto end;
        }
        video_dst_bufsize = ret;
    }

    //4.打开音频解码器并初始化，得到解码音频的AVCodecContext结构体对象
    if (open_codec_context(&audio_stream_idx, &audio_dec_ctx, fmt_ctx, AVMEDIA_TYPE_AUDIO) >= 0) {
        audio_stream = fmt_ctx->streams[audio_stream_idx];
        audio_dst_file = fopen(audio_dst_filename, "wb");
        if (!audio_dst_file) {
            fprintf(stderr, "Could not open destination file %s\n", audio_dst_filename);
            ret = 1;
            goto end;
        }
    }

    /* dump input information to stderr */
    av_dump_format(fmt_ctx, 0, src_filename, 0);

    if (!audio_stream && !video_stream) {
        fprintf(stderr, "Could not find audio or video stream in the input, aborting\n");
        ret = 1;
        goto end;
    }

    //5.分配存储解码后帧的内存空间
    frame = av_frame_alloc();
    if (!frame) {
        fprintf(stderr, "Could not allocate frame\n");
        ret = AVERROR(ENOMEM);
        goto end;
    }

    //6.分配存储解码前包的内存空间
    av_init_packet(&pkt);
    pkt.data = NULL;
    pkt.size = 0;

    //7.源源不断的从原始输入文件中读取音视频包，并解码。
    //  存储解码后的帧数据的变量frame是全局变量，在解码函数内直接使用。
    while (av_read_frame(fmt_ctx, &pkt) >= 0) {
        if (pkt.stream_index == video_stream_idx)
            ret = decode_packet(video_dec_ctx, &pkt);
        else if (pkt.stream_index == audio_stream_idx)
            ret = decode_packet(audio_dec_ctx, &pkt);
        av_packet_unref(&pkt);
        if (ret < 0)
            break;
    }

    //8.最后一定要清空编码器缓冲区,发送NULL frame编码器进入flush模式。
    if (video_dec_ctx)
        decode_packet(video_dec_ctx, NULL);
    if (audio_dec_ctx)
        decode_packet(audio_dec_ctx, NULL);

    //9.解码成功后，打印播放解码后文件命令的提示信息
    printf("Demuxing succeeded.\n");

    if (video_stream) {
        printf("Play the output video file with the command:\n"
               "ffplay -f rawvideo -pix_fmt %s -video_size %dx%d %s\n",
               av_get_pix_fmt_name(pix_fmt), width, height,
               video_dst_filename);
    }

    if (audio_stream) {
        enum AVSampleFormat sfmt = audio_dec_ctx->sample_fmt;
        int n_channels = audio_dec_ctx->channels;
        const char *fmt;

        if (av_sample_fmt_is_planar(sfmt)) {
            const char *packed = av_get_sample_fmt_name(sfmt);
            printf("Warning: the sample format the decoder produced is planar "
                   "(%s). This example will output the first channel only.\n",
                   packed ? packed : "?");
            sfmt = av_get_packed_sample_fmt(sfmt);
            n_channels = 1;
        }

        if ((ret = get_format_from_sample_fmt(&fmt, sfmt)) < 0)
            goto end;

        printf("Play the output audio file with the command:\n"
               "ffplay -f %s -ac %d -ar %d %s\n",
               fmt, n_channels, audio_dec_ctx->sample_rate,
               audio_dst_filename);
    }

end:
    avcodec_free_context(&video_dec_ctx);
    avcodec_free_context(&audio_dec_ctx);
    avformat_close_input(&fmt_ctx);
    if (video_dst_file)
        fclose(video_dst_file);
    if (audio_dst_file)
        fclose(audio_dst_file);
    av_frame_free(&frame);
    av_free(video_dst_data[0]);

    return ret < 0;
}
